Process for making a fibrous building material



Patented June 14, 1932 PATENT; OFFICE 'EMIL C. LOETSCHER, OF DUBUQUE, IOWA PROCESS FOR MAKING A FIBROUS BUILDING MATERIAL N Drawing.

This invention relates to improvements in processes for making a fibrous building material, and more particularly a hard and wood-like composition of cellulose fibre which can be used in place of natural wood in the manufacture of mill-work and interior finishing materials such as doors, door panels, trim, mouldings and the like.

Heretofore, the use of wood pulp or cellulose fibre-has been confined largely to the manufacture of various forms .of pulp or fibre board employed extensively as a wall covering or insulating material. Such materials, however, have neither the strength or density to be used in place of wood, nor have they the thickness and surface finish for the fabrication of such articles as door panels and the like".

The usual process of manufacturing pulp board consists briefly, in forming a mat on a rotary cylindric screen immersed in a vat of wet'pulp, a vacuum being maintained interiorthe cylinder so that as the cylinder is rotated, a mat is built up on the surface which is then removed, placed in a press and reduced to its final thickness at the same time being heated to dryness for a period of from thirty minutes to two hours, depending on the temperature used. This method, while satisfactory for thin materials used for insulating board and the like, has its limita tions and objections. In the first place, the thickness of the mat initially formed of wet pulp is limited to an inch or so, and hence when compressed to or of an inch there is not sufiicient strength in the material to serve the purposes here intended. Again, the pressing and drying of the mat is accomplished in a single continuous operation, tak- 0 ing upwardly of two hours, the moisture being first converted into steam which escapes through a perforated plate pressing against one face of the board, and leaving an impression which renders it unfit for a finished surface.

The purpose, therefore, of the present invention is to provide an improved process which eliminates the objections to and high cost of operating under the processes now generally followed, and further, a process Application filed July 12, 1929. Serial No. 377,918.

which will make possible the manufacture of satisfactory fibrous wood substitute mate rial on a profitable commercial scale.

The following is a description of the preferred method:

The initial step ismanifestly the preparation of the pulp, which may be made from cornstalk, wood, or any other cellulose fibre material. For preparing a mat of the desired thickness, a frame or form is made into which the pulp is introduced to the desiredthickness, the shape and horizontal dimensions of the frame being substantially the same as the article or piece to be produced, such as a board or panel. The form is placed upon a platform having a perforated or wire mesh surface to form a filter screen and an enclosed space below the screen which is maintained below atmospheric pressure by a suitable vacuum pump connected therewith. The form is filled with the pulp to the required depth depending on the ultimate thickness of the article to be made and is then compressed by applyin pressure to a follow board laid on top of the pulp and pressing it down with sufficient force to squeeze out the excess water, say from 40% to the water passingthrough the filter screen at the bottom assisted by the reduced pressure below. This operation takes but a few minutes and forms a mat of pulp from which considerable part of the water has been removed but Which has not been compressed to any appreciable degree.

The mat is then removed from the frame and placed in a hydraulic press equipped with especially designed platens, the same being hollow to permit steam under pressure to pass through them for heating and likewise water for cooling. The pressure is applied vertically and in a direction to compress the mat to approximately its ultimate thickness and at the same time the platens are heated by introducing steam at from 50 to 100 pounds pressure. To prevent the material from expanding laterally While the pressure is being applied the edges of the platens are preferably enclosed within a steel frame.

The pressure and heat are not maintained for any extended period, however, but only for a very short time, from three to five minutes. During this period more of the moisture is driven from the mat, leaving in the neighborhood of 15 to 20%, whereupon the steam is shut off and cooling water circulated through the platens, the pressure still being applied until the mat, now compresed to its approximate final thickness, is cooled down to the normal room temperature, or below.

It is to be observed that the heat is not maintained long enough to convert the moisture in the pulp mat Into steam in sufiicient volume or at such a pressure as to necessitate the perforating of either platen in order to permit it to escape, and consequently the surfaces of both latens are perfectly smooth as are those of t e mat when removed from the press.

It might be explained that excessive heating at this stage of the process might readily be the cause of a violent eruption due to the steam generated between the platens, and it is for this reason that means of escape must be provided where the complete drying is undertaken while the material is in the press, and hence the reason for the imprint of screen or perforation on the surface of the material made by the usual methods.

After the mat or layer of compressed fibres has been com ressed in the presence of heat and then coo ed, it is taken from the press and placed in a drying room or chamber, not unlike a drying kiln where it is allowed to remain in a temperature of from 250 F. to 27 5 F. until it is substantially dry, that is, with only from 2% to 5% of moisture remain ing. The drying room is designed to handle a considerable quantity of the layers of material as it comes from one or more of the presses, being stacked with separating strips between so that they may dry uniformly and therefore without excessive warping.

However, there is every possibility that there will be some warping and perhaps unevenness in the surface of the material after it has been dried, so that as the final step in the process, the boards or panels as the case may be, are again placed in the presses where they are subjected to a second pressure and heat treatment, this time thepressure being increased somewhat as well as the temperature to which it is heated. This final pressing operation which is carried on for about ten minutes, permanently sets the fibres and removes any inequality in the thickness or uneveness in the surfaces of thefinished prodnot.

Thus it is seen that the process includes the steps of preparing the mat in a form arranged to remove the excess water by pressure assisted by a partial vacuum, the initial compression of the mat in a press for a relatively short period to reduce it to approximately its final thickness and in the presenceof heat sufficient to drive off still more of the moisture, the cooling of the compressed mat while under the complete drying of-the material in a drying chamber, and a second and final pressure and heat treatment which sets the a drying oven, and moreover, can only handle One board or panel at one time, it is quite obvious that the cost of manufacture becomes prohibitive if a single press is occupied for upwardly of two hours in the processin of a single board where the compressing an drying is carried on as a single continuous operation. Furthermore, the complete drying of a board in a press is complicated by the fact that the material is confined between two plates and therefore the moisture has only a limited avenue of escape, namely around the edges and hence the conditions are at the very outset not conducive to rapid and efficient drying. Thus by subjecting the material to an initial pressure and heat treatment for a relatively short period of time sufficient to reduce the same to the required density but without carryingthe step to, the extent of complete drying, and then removing it to a drying oven, the output can be greatly'increased and at a considerably less cost.

The length of time required for the initial as well as the final pressing operation, is determined by the density desired in the particular material being made and the temperature of the steam admitted to the platens, for manifestly the greater the compressive force the denser and stronger will be the resulting product,-and the higher the temperature, the I minutes for the initial press operation and ten minutes for the final or fifteen minutes in all, as compared with from thirty minutes to two hours required in any other manufacturing process of which I have knowledge.

The practicability of the process as set forth is attributable to the'fact that complete dryingunder pressure has been found by experiment to be unnecessary in order to compress the pulp to a condition such that it will not expand after the pressure is removed although still containin a substantial percentage of moisture. pulp of cellulose fibrous material will be found to be composed of a multitude of separate fibres each surrounded by a film of water. Experiment has shown that if pressure and heat'are applied to the pulp in the form of a mat, in an amount or degree suflicient to remove or break the film characteristics of the fibre structure and its,

behavior under pressure which make it possible to introduce the rocess into commercial usage in the manufiacture of a cellulose fibrous material for the particular uses herein enumerated. v

Manifestly, a number of refinements in the process may be introduced to improve the quality of the product, but which do not materially alter the working of the process. For instance, in the preparation of the mat, different grades or texture of pulp may be used, as for instance, a fine grade for the surface layer and a coarser grade for the inner core or base. Again, the material may be waterproofed by adding a suitable resinous compound to the pulp, and,*if an exceptionally smooth surface is desired, polished steel plates may be placed between the material and platens in the final compressing operation. It is also possible to color the material by adding a mineral pigment to the pulp or merely to the surface coating or layer in case it is not necessary to color the material throughout. And finally, the surfaces may be treated with a varnish, suchas bakelite', before it is placed in the drying room with the result that when finally heated in the press, a hard infusiblc coating is produced.

As already suggested, a niaterial made by this process can be successfully used in place of wood for all kinds of millwork and interior woodwork, for which uses it is superior to wood in that it does not split or crack when being nailed in place and undergoes practically no shrinkage or-warping. The surfaces can be decorated by painting or enamelling,

and even-natural wood graining faithfully reproduced without appreciable increase in cost.

In view, therefore, of the numerous refinements mentioned and other modifications which may be introduced without departing from the spirit of the invention, I do not wish to be limited in the scope thereof except in so far as it is set forth in the appended claims.

, of time sufiicient to remove a predetermined portion of the moisture-and reduce the same to substantially its final thickness and density, releasing the material from compression and reducing the'same to substantial dryness; and again compressing the material to its final thickness and density.

2. The process of manufacturing a fibrous building materialconsisting of preparing a relatively thick mat of moist fibrous material, placing the mat in a press and compressing the same in the presence of heat for a period of time sufiicient to permanently set the fibres without completely removing the moisture, cooling the partially compressed material under pressure, removing the material from the press and reducing it to complete dryness in a heated enclosure, and again compressing the dried material to its final thickness and density.

3. The process of making a material of a cellulose fibrous substance, consisting of forming a mat of the moist fibre pulp, compressing the mat in a press for a relatively short period in the presence of heat suficient to partially dry the material and set the fibres against subsequentexpansion, cooling said mat While under pressure, removing the partially dried material from the press and heating the same to substantial dryness in a drying. enclosure, and again subjecting the material to pressure and heat in said press to reduce the same to its final thickness and density 4. The process of making a material of a cellulose fibrous substance, consisting of preparing a mat of the pulp from which the excess water has been removed, compressing the mat in a press for a relatively short period in the presence of heat sufiicient to set the fibres against subsequent expansion, cooling said mat while under pressure, transferring the compressed material from the press to a heated enclosure and drying the same to substantial dryness therein, and subjecting the dried material to further compression, whereby the same is reduced to its final density and thickness.

5. The process of making a wood substitute material of a cellulose fibrous substance, consisting of preparing a mat substantially thicker than the final product, and containing substantially 50% of the moisture content, compressing the mat in a press for a short period of time in the presence of heat sufiicient to reduce the moisture content to approximately 20%, and to reduce the mat to substantially its final thickness and density, cooling the material while under pressure, removing the material from the press and artificially drying the same to substantial dryness, and again subjecting the material to pressure in the press for a slightly longer period whereb the same is reduced to its final thickness an density.

Signed at Dubuque, 1a., this 8th day of July, 1929. EMIL O. LOETSCHER- roe ice

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